Myeloid-like tumor hybrid cells in bone marrow promote progression of prostate cancer bone metastasis.

BACKGROUND: Bone metastasis is the leading cause of death in patients with prostate cancer (PCa) and currently has no effective treatment. Disseminated tumor cells in bone marrow often obtain new characteristics to cause therapy resistance and tumor recurrence. Thus, understanding the status of disseminated prostate cancer cells in bone marrow is crucial for developing a new treatment. METHODS: We analyzed the transcriptome of disseminated tumor cells from a single cell RNA-sequencing data of PCa bone metastases. We built a bone metastasis model through caudal artery injection of tumor cells, and sorted the tumor hybrid cells by flow cytometry. We performed multi-omics analysis, including transcriptomic, proteomic and phosphoproteomic analysis, to compare the difference between the tumor hybrid cells and parental cells. In vivo experiments were performed to analyze the tumor growth rate, metastatic and tumorigenic potential, drug and radiation sensitivity in hybrid cells. Single cell RNA-sequencing and CyTOF were performed to analyze the impact of hybrid cells on tumor microenvironment. RESULTS: Here, we identified a unique cluster of cancer cells in PCa bone metastases, which expressed myeloid cell markers and showed a significant change in pathways related to immune regulation and tumor progression. We found that cell fusion between disseminated tumor cells and bone marrow cells can be source of these myeloid-like tumor cells. Multi-omics showed the pathways related to cell adhesion and proliferation, such as focal adhesion, tight junction, DNA replication, and cell cycle, were most significantly changed in these hybrid cells. In vivo experiment showed hybrid cells had a significantly increased proliferative rate, and metastatic potential. Single cell RNA-sequencing and CyTOF showed tumor-associated neutrophils/monocytes/macrophages were highly enriched in hybrid cells-induced tumor microenvironment with a higher immunosuppressive capacity. Otherwise, the hybrid cells showed an enhanced EMT phenotype with higher tumorigenicity, and were resistant to docetaxel and ferroptosis, but sensitive to radiotherapy. CONCLUSION: Taken together, our data demonstrate that spontaneous cell fusion in bone marrow can generate myeloid-like tumor hybrid cells that promote the progression of bone metastasis, and these unique population of disseminated tumor cells can provide a potential therapeutic target for PCa bone metastasis.

Energy saver: Monocytes hibernate in bone marrow upon fasting.

Immune functions are influenced by the nutritional state. In a recent publication in Immunity, Janssen et al. unveil that a fasting-induced glucocorticoid release makes monocytes move from blood into the bone marrow. Upon refeeding, these chronologically older monocytes are again released and exert detrimental effects during bacterial infection.

A Case of AML1-ETO Positive Acute Myeloid Leukemia Morphologically Similar to Chronic Myelogenous Leukemia.

BACKGROUND: The goal was to study the role of the morphology, immunophenotype, karyotype and fusion gene expression in a patient with diagnosis of AML1-ETO positive acute myeloid leukemia. METHODS: A case of AML1-ETO positive acute myeloid leukemia morphologically similar to chronic myelogenous leukemia was reported. The results of the morphology, immunophenotype, karyotype and fusion gene expression were analyzed by reviewing relevant literature. RESULTS: The patient was a young boy, at the age of 13, with clinical manifestations of intermittent fatigue and fever. Blood routine: White blood cell 142.6 x 109/L, Red blood cell 0.89 x 1012/L, Hemoglobin 41 g/L, Platelet 23 x 109/L, primitive cells account for 5%. Bone marrow smear: Granulocyte system hyperplasia is obvious, visible at each stage, primitive cells account for 17%, eosinophils, basophils, and phagocytic blood cells were observed. Flow cytometry showed myeloid primitive cell population was 4.14%, immature and mature granulocytes cell population was 85.22%, and eosinophil cell population was 0.61%. The results showed that the proportion of myeloid primitive cell was high, the expression of CD34 was enhanced, the expression of CD117 was partially absent, the expression of CD38 was weakened, the expression of CD19 was weak, and a few cells expressed CD56, and the phenotype was abnormal. The proportion of granulocyte series increased and the nucleus shifted to the left. The proportion of erythroid series was decreased, and the expression of CD71 was weakened. The results of fusion gene showed AML1-ETO positive. Karyotype analysis showed clonogenic abnormality t(8;21)(q22;q22). CONCLUSIONS: The peripheral blood and bone marrow images of patients with t(8;21)(q22;q22) AML1-ETO positive are the manifestations of chronic myelogenous leukemia, suggesting that cytogenetics and molecular genetics play an irreplaceable role in the diagnosis of acute myeloid leukemia, and the comprehensive diagnostic efficiency is significantly better than that of morphology.

One Stage Masquelets Technique: Evaluation of Different Forms of Membrane Filling with and without Bone Marrow Mononuclear Cells (BMC) in Large Femoral Bone Defects in Rats.

The classic two-stage masquelet technique is an effective procedure for the treatment of large bone defects. Our group recently showed that one surgery could be saved by using a decellularized dermis membrane (DCD, Epiflex, DIZG). In addition, studies with bone substitute materials for defect filling show that it also appears possible to dispense with the removal of syngeneic cancellous bone (SCB), which is fraught with complications. The focus of this work was to clarify whether the SCB can be replaced by the granular demineralized bone matrix (g-DBM) or fibrous demineralized bone matrix (f-DBM) demineralized bone matrix and whether the colonization of the DCD and/or the DBM defect filling with bone marrow mononuclear cells (BMC) can lead to improved bone healing. In 100 Sprague Dawley rats, a critical femoral bone defect 5 mm in length was stabilized with a plate and then encased in DCD. Subsequently, the defect was filled with SCB (control), g-DBM, or f-DBM, with or without BMC. After 8 weeks, the femurs were harvested and subjected to histological, radiological, and biomechanical analysis. The analyses showed the incipient bony bridging of the defect zone in both groups for g-DBM and f-DBM. Stability and bone formation were not affected compared to the control group. The addition of BMCs showed no further improvement in bone healing. In conclusion, DBM offers a new perspective on defect filling; however, the addition of BMC did not lead to better results.

A longitudinal multidimensional rehabilitation program for patients undergoing allogeneic blood and marrow transplantation (CaRE-4-alloBMT): Protocol for a phase II feasibility pilot randomized controlled trial.

BACKGROUND: Allogeneic blood and marrow transplantation (alloBMT) is a curative treatment for blood cancers associated with various treatment-related adverse events and morbidities. Current rehabilitation programs are limited for patients undergoing alloBMT and research is urgently needed to test the acceptability and effectiveness of these programs. In response, we developed a 6-month multidimensional longitudinal rehabilitation program that spans from pre transplant to 3 months post transplant discharge (CaRE-4-alloBMT). METHODS: This study is a phase II randomized controlled trial (RCT) conducted at the Princess Margaret Cancer Centre in patients undergoing alloBMT. A total of 80 patients stratified by frailty score will be randomized to receive usual care (n = 40) or CaRE-4-alloBMT plus usual care (n = 40). The CaRE-4-alloBMT program includes individualized exercise prescriptions, access to online education through a dedicated self-management platform, wearable technology for remote monitoring, and remote tailored clinical support. Feasibility will be assessed by examining the recruitment and retention rates and adherence to the intervention. Safety events will be monitored. Acceptability of the intervention will be assessed through qualitative interviews. Secondary clinical outcomes will be collected through questionnaires and physiological assessments at baseline (T0, 2-6 weeks pre-transplant), transplant hospital admission (T1), hospital discharge (T2), and 3 months post-discharge (T3). CONCLUSION: This pilot RCT study will determine the feasibility and acceptability of the intervention and study design and will inform full-scale RCT planning.

Evidence for EpCAM and Cytokeratin Expressing Epithelial Cells in Normal Human and Murine Blood and Bone Marrow.

Epithelial cells have been identified in the blood and bone marrow of patients with cancer and other diseases. However, the presence of normal epithelial cells in the blood and bone marrow of healthy individuals has yet to be identified in a consistent way. Presented here is a reproducible method for isolating epithelial cells from healthy human and murine blood and bone marrow (BM) using flow cytometry and immunofluorescence (IF) microscopy. Epithelial cells in healthy individuals were first identified and isolated via flow cytometry using epithelial cell adhesion molecule (EpCAM). These EpCAM+ cells were confirmed to express keratin using immunofluorescence microscopy in Krt1-14;mTmG transgenic mice. Human blood samples had 0.18% ± 0.0004 EpCAM+ cells (SEM; n=7 biological replicates, 4 experimental replicates). In human BM, 3.53% ± 0.006 (SEM; n=3 biological replicates, 4 experimental replicates) of mononuclear cells were EpCAM+. In mouse blood, EpCAM+ cells constituted 0.45% ± 0.0006 (SEM; n=2 biological replicates, 4 experimental replicates), and in mouse BM, 5.17% ± 0.001 (SEM; n=3 biological replicates, 4 experimental replicates) were EpCAM+. In mice, all the EpCAM+ cells were immunoreactive to pan-cytokeratin, as determined by IF microscopy. Results were confirmed using Krt1-14;mTmG transgenic mice, with low (8.6 native GFP+ cells per 106 cells analyzed; 0.085% of viable cells), but significant numbers (p < 0.0005) of GFP+ cells present in normal murine BM, that were not the result of randomness compared with multiple negative controls. Further, EpCAM+ cells in mouse blood were more heterogeneous than CD45+ cells (0.58% in BM; 0.13% in blood). These observations conclude that cells expressing cytokeratin proteins are reproducibly detectable among mononuclear cells from human and murine blood and BM. We demonstrate a method of tissue harvesting, flow cytometry, and immunostaining that can be used to identify and determine the function of these pan-cytokeratin epithelial cells in healthy individuals.

Isolation, In Vitro Differentiation, and Culture of Murine Megakaryocytes From Fetal Liver and Adult Bone Marrow.

Megakaryocytes (MKs) are the source of circulating platelets and are readily recognized by their large size and distinctive morphology. Their poor representation in hematopoietic tissues often requires enrichment or considerable ex vivo expansion to generate cells for biochemical and cell biological studies. These experimental protocols describe the enrichment of primary MKs directly from the murine bone marrow as well as in vitro differentiation of fetal liver- or bone marrow-derived hematopoietic stem cells into MKs. Although in vitro-differentiated MKs are not synchronized in their maturation, they can be enriched over an albumin density gradient, and one-third to one-half of recovered cells will typically elaborate proplatelets. Support protocols describe methods for preparing fetal liver cells, identifying mature rodent MKs by staining for flow cytometry analysis, and immunofluorescence staining of fixed MKs for confocal laser scanning microscopy. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Isolation of mature bone marrow megakaryocytes by magnetic-activated cell sorting Basic Protocol 2: Preparation of a megakaryocyte suspension culture from murine fetal livers or lineage-depleted adult bone marrow Support Protocol 1: Preparation of a single-cell suspension from murine fetal livers for megakaryocyte culture Support Protocol 2: Megakaryocyte culture from lineage-depleted murine bone marrow Support Protocol 3: Quality control of megakaryocyte culture with flow cytometry Support Protocol 4: Immunofluorescence staining of megakaryocytes for detection with confocal laser scanning microscopy.

Intra-marrow penetrations and root coverage outcomes: a systematic review.

BACKGROUND: Intra-marrow penetrations (IMPs) have been performed during guided tissue regeneration (GTR) procedures with reported clinical benefits. The aim of this systematic review was to investigate the use and effect of IMPs during root coverage procedures. METHOD: A broad search for human and animal studies was performed on PubMed, Cochrane Database of Systematic Reviews and Cochrane Central Registry of Controlled Trials and Web of Science, following a registered review protocol (PROSPERO). All prospective study designs, case series and case reports on gingival recession treatment (follow-up ≥ 6 months) that employed IMPs were included. Root coverage, complete root coverage prevalence, and adverse effects were recorded, and risk of bias was assessed. RESULTS: Of 16,181 screened titles, 5 articles (all of them human studies) met inclusion criteria. All studies (including two randomized clinical trials) treated Miller class I and II recession defects, using coronally advanced flap with IMPs alone or in conjunction with GTR protocols. Therefore, all treated defects received IMPs and no studies compared protocols with and without IMPs. Outcomes were indirectly compared with existing root coverage literature. Mean root coverage was 2.7 mm and 68.5% at 6.8 months (median: 6 months, range 6-15 months) for sites treated with IMPs. CONCLUSION: IMPs are rarely used during root coverage procedures, have not been associated with intra-surgical or wound healing adverse effects and have not been investigated as independent factor. Future clinical studies are needed to directly compare treatment protocols with and without IMPs and investigate the potential benefits of IMPs for root coverage.

An in vivo humanized model to study homing and sequestration of Plasmodium falciparum transmission stages in the bone marrow.

Introduction: Recent evidence suggests that the bone marrow (BM) plays a key role in the diffusion of P. falciparum malaria by providing a "niche" for the maturation of the parasite gametocytes, responsible for human-to-mosquito transmission. Suitable humanized in vivo models to study the mechanisms of the interplay between the parasite and the human BM components are still missing. Methods: We report a novel experimental system based on the infusion of immature P. falciparum gametocytes into immunocompromised mice carrying chimeric ectopic ossicles whose stromal and bone compartments derive from human osteoprogenitor cells. Results: We demonstrate that immature gametocytes home within minutes to the ossicles and reach the extravascular regions, where they are retained in contact with different human BM stromal cell types. Discussion: Our model represents a powerful tool to study BM function and the interplay essential for parasite transmission in P. falciparum malaria and can be extended to study other infections in which the human BM plays a role.

Insights into IGH clonal evolution in BCP-ALL: frequency, mechanisms, associations, and diagnostic implications.

Introduction: The malignant transformation leading to a maturation arrest in B-cell precursor acute lymphoblastic leukemia (BCP-ALL) occurs early in B-cell development, in a pro-B or pre-B cell, when somatic recombination of variable (V), diversity (D), and joining (J) segment immunoglobulin (IG) genes and the B-cell rescue mechanism of VH replacement might be ongoing or fully active, driving clonal evolution. In this study of newly diagnosed BCP-ALL, we sought to understand the mechanistic details of oligoclonal composition of the leukemia at diagnosis, clonal evolution during follow-up, and clonal distribution in different hematopoietic compartments. Methods: Utilizing high-throughput sequencing assays and bespoke bioinformatics we identified BCP-ALL-derived clonally-related IGH sequences by their shared 'DNJ-stem'. Results: We introduce the concept of 'marker DNJ-stem' to cover the entirety of, even lowly abundant, clonally-related family members. In a cohort of 280 adult patients with BCP-ALL, IGH clonal evolution at diagnosis was identified in one-third of patients. The phenomenon was linked to contemporaneous recombinant and editing activity driven by aberrant ongoing DH/VH-DJH recombination and VH replacement, and we share insights and examples for both. Furthermore, in a subset of 167 patients with molecular subtype allocation, high prevalence and high degree of clonal evolution driven by ongoing DH/VH-DJH recombination were associated with the presence of KMT2A gene rearrangements, while VH replacements occurred more frequently in Ph-like and DUX4 BCP-ALL. Analysis of 46 matched diagnostic bone marrow and peripheral blood samples showed a comparable clonal and clonotypic distribution in both hematopoietic compartments, but the clonotypic composition markedly changed in longitudinal follow-up analysis in select cases. Thus, finally, we present cases where the specific dynamics of clonal evolution have implications for both the initial marker identification and the MRD monitoring in follow-up samples. Discussion: Consequently, we suggest to follow the marker DNJ-stem (capturing all family members) rather than specific clonotypes as the MRD target, as well as to follow both VDJH and DJH family members since their respective kinetics are not always parallel. Our study further highlights the intricacy, importance, and present and future challenges of IGH clonal evolution in BCP-ALL.

Association of mesenchymal stem cells derived from bone marrow and adipose tissue enhances bone repair in rat calvarial defects.

Aim: We evaluated the bone repair induced by MSCs from adipose tissue (AT-MSCs) and bone marrow (BM-MSCs) injected into rat calvarial defects at two time points. Methods & results: Both cell populations expressed MSC surface markers and differentiated into adipocytes and osteoblasts. µCT showed that the combination of cells from distinct sources exhibited synergistic effects to increase bone repair with an advantage when BM-MSCs were injected prior to AT-MSCs. The higher osteogenic potential of these MSC combinations was demonstrated using an in vitro coculture system where BM-MSCs and AT-MSCs association induced higher ALP activity in MC3T3-E1 cells. Conclusion: Our findings may drive new approaches to treat bone defects and shed light on the complexity of the mechanisms involved in bone regeneration.

We evaluated the bone repair induced by cells that can develop into different types of cells (stem cells) derived from fat and spongy tissue inside the large bones and injected into defects created in rat skulls. Cells derived from both tissues developed into fat cells and bone-forming cells. The combination of cells from fat and spongy tissue exhibited cooperative effects to increase bone repair with an advantage when cells from spongy tissue were injected prior to cells from fat. Our findings may contribute to stablish new therapies based on the use of cells to treat large bone defects.

Impact of the Extremities Positioning on the Set-Up Reproducibility for the Total Marrow Irradiation Treatment.

Total marrow (lymph node) irradiation (TMI/TMLI) delivery requires more time than standard radiotherapy treatments. The patient's extremities, through the joints, can experience large movements. The reproducibility of TMI/TMLI patients' extremities was evaluated to find the best positioning and reduce unwanted movements. Eighty TMI/TMLI patients were selected (2013-2022). During treatment, a cone-beam computed tomography (CBCT) was performed for each isocenter to reposition the patient. CBCT-CT pairs were evaluated considering: (i) online vector shift (OVS) that matched the two series; (ii) residual vector shift (RVS) to reposition the patient's extremities; (iii) qualitative agreement (range 1-5). Patients were subdivided into (i) arms either leaning on the frame or above the body; (ii) with or without a personal cushion for foot positioning. The Mann-Whitney test was considered (p < 0.05 significant). Six-hundred-twenty-nine CBCTs were analyzed. The median OVS was 4.0 mm, with only 1.6% of cases ranked < 3, and 24% of RVS > 10 mm. Arms leaning on the frame had significantly smaller RVS than above the body (median: 8.0 mm/6.0 mm, p < 0.05). Using a personal cushion for the feet significantly improved the RVS than without cushions (median: 8.5 mm/1.8 mm, p < 0.01). The role and experience of the radiotherapy team are fundamental to optimizing the TMI/TMLI patient setup.

[Forensic pathological diagnostics of rare T-cell leukemia in re-examination]. / Sudebno-gistologicheskaya diagnostika redkogo T-kletochnogo leikoza pri proizvodstve povtornoi ekspertizy.

A forensic pathological case of rare T-cell leukemia is reported. Autopsy samples (paraffine blocks and slides) from 32 years old female with long-term existing anemia and leukopenia, number of chronic inflammatory diseases, died from fulminant pneumonia, were presented for forensic pathological re-examination. A routine histological examination was done using standard H&E stain. Additionally, we used IHC stain with antibodies to CD3 and CD20 when examining bone marrow and liver samples. The T-cell infiltration in bone marrow (interstitial and intrasinusoidal type) were found. The next step was IHC bone marrow examination with CD4, CD5, CD8, CD56 antibodies. We concluded that the patient had unrecognized T-cell leukemia, based on anamnestical, clinical data and results of our histological and IHC examination. In this case, the T-cell leukemia was not found neither vitally nor at primary forensic pathological examination after autopsy. The necessity of minimal IHC stain sets usage in primary forensic pathology units and IHC's decisive role in bone marrow pathological examination are discussed.

Bone marrow endosteal stem cells dictate active osteogenesis and aggressive tumorigenesis.

The bone marrow contains various populations of skeletal stem cells (SSCs) in the stromal compartment, which are important regulators of bone formation. It is well-described that leptin receptor (LepR)+ perivascular stromal cells provide a major source of bone-forming osteoblasts in adult and aged bone marrow. However, the identity of SSCs in young bone marrow and how they coordinate active bone formation remains unclear. Here we show that bone marrow endosteal SSCs are defined by fibroblast growth factor receptor 3 (Fgfr3) and osteoblast-chondrocyte transitional (OCT) identities with some characteristics of bone osteoblasts and chondrocytes. These Fgfr3-creER-marked endosteal stromal cells contribute to a stem cell fraction in young stages, which is later replaced by Lepr-cre-marked stromal cells in adult stages. Further, Fgfr3+ endosteal stromal cells give rise to aggressive osteosarcoma-like lesions upon loss of p53 tumor suppressor through unregulated self-renewal and aberrant osteogenic fates. Therefore, Fgfr3+ endosteal SSCs are abundant in young bone marrow and provide a robust source of osteoblasts, contributing to both normal and aberrant osteogenesis.

Isolation and Cryopreservation of Mononuclear Cells from Peripheral Blood and Bone Marrow of Blood Cancer Patients.

Peripheral blood and bone marrow aspirates are routinely obtained from blood cancer patients for diagnostic investigations and provide an accessible source of patient-specific cancer cells, as well as non-malignant cells, for research proposes. The simple and reproducible method presented here allows isolation of viable mononuclear cells, including malignant cells, from fresh peripheral blood or bone marrow aspirates using density gradient centrifugation. The cells obtained using the protocol described can be further purified for a variety of cellular, immunological, molecular, and functional assays. In addition, these cells can be cryopreserved and bio-banked for future research studies.

Immunomodulatory effects of bone marrow-derived Mesenchymal stem cells on BALB/c mice model with induced Systemic lupus erythematosus (SLE).

  Systemic lupus erythematosus (SLE) is an autoimmune inflammatory disease that causes acute inflammation in most body tissues. The current study aims to determine levels of some cytokines and chemokines in BALB/c mice with SLE and treatment by using BALB/c Mesenchymal stem cells (BM-MSCs). Forty BALB/c male mice were divided into four groups equally. The first and second groups received activated lymphocyte-derived DNA (ALD DNA) for induction of SLE. The second group received BM-MSCs/IV after the appearance of SLE clinical signs. The third group received BM-MSCs only, while the fourth group (control group) received PBS. All the study groups examine levels of IL-10, IL-6, TGFß1, VEGF, CCL-2, CCL-5/RANTES, IFNγ, and ICAM -1 by ELISA kits. The cytokines levels are determined in all the study groups. There was a significant increase in ANA and anti-dsDNA levels in the first group, while there was a decrease in the second group (treatment by BM-MSCs). There is no significant difference between the third and control groups in ANA and anti-dsDNA levels. The first group showed a significant increase in IL-6, CCL-5/RANTES, VEGF, ICAM, CCL-2, and IFNγ levels and a decrease in IL-10 and TGFß1. The second group showed low levels of IL-6, CCL-5/RANTES, VEGF, ICAM, CCL-2/MCP-1, and IFNγ but a high level of IL-10 and TGFß1 as compared with the control group. The third group has no significant differences from the control group in all the tested parameters. BM-MSCs have an essential therapeutic role in the functional regulation of cytokines and chemokines in mice with SLE.

Biophysical cues of bone marrow-inspired scaffolds regulate hematopoiesis of hematopoietic stem and progenitor cells.

Hematopoietic stem cells (HSCs) are adult multipotential stem cells with the capacity to differentiate into all blood cells and immune cells, which are essential for maintaining hematopoietic homeostasis throughout the lifespan and reconstituting damaged hematopoietic system after myeloablation. However, the clinical application of HSCs is hindered by the imbalance of its self-renewal and differentiation during in vitro culture. Considering the fact that HSC fate is uniquely determined by natural bone marrow microenvironment, various elaborate cues in this hematopoietic micro-niche provide an excellent reference for the regulation of HSCs. Inspired by the bone marrow extracellular matrix (ECM) network, we designed degradable scaffolds by orchestrating the physical parameters to investigate the decoupling effects of Young's modulus and pore size of three-dimensional (3D) matrix materials on the fate of hematopoietic stem and progenitor cells (HSPCs). We ascertained that the scaffold with larger pore size (80 µm) and higher Young's modulus (70 kPa) was more favorable for HSPCs proliferation and the maintenance of stemness related phenotypes. Through in vivo transplantation, we further validated that scaffolds with higher Young's modulus were more propitious in maintaining the hematopoietic function of HSPCs. We systematically screened an optimized scaffold for HSPC culture which could significantly improve the cell function and self-renewal ability compared with traditional two-dimensional (2D) culture. Together, these results indicate the important role of biophysical cues in regulating HSC fate and pave the way for the parameter design of 3D HSC culture system.

Association of pre-treatment bone marrow morphology and achievement of BCR-ABL1 transcript milestones in CML.

Chronic myeloid leukemia (CML) is characterized by the fusion gene BCR-ABL1 which encodes aberrantly functioning tyrosine kinase. Treatment with tyrosine kinase inhibitors (TKI) is a landmark of CML management and the main goal is to achieve major molecular response (MMR) which is defined as BCR-ABL1IS ≤ 0.1 % at 12 months of therapy. The aim of this study is to analyze histologic features of bone marrow (BM) in CML patients at the time of diagnosis and compare it to the level of BCR-ABL1IS transcript at 3 (BCR-ABL1IS ≤10 % early molecular response; EMR) and 12 months (MMR) as well as to so called molecularly undetectable leukemia (MUL) to see weather bone marrow morphology can be of value in predicting achievement molecular response milestones. Thirty-two bone marrow biopsies of CML patients, prior TKI therapy, were re-evaluated and CD34 immunohistochemistry was performed to examine microvessel density (MVD) and microvessel area (MVA) and subsequently compared it to the level of BCR-ABL1IS transcript. This study showed statistically significant association between BM hypercellularity and EMR (p = 0.048) and MUL (p = 0.034), peri-trabecular adipocyte distribution and EMR and MUL (p = 0.027 and p = 0.011, respectively), MMR and bone marrow fibrosis (p = 0.029), loose megakaryocyte clustering and EMR and MUL (p = 0.004 and p = 0.018, respectively), absence of naked nuclei and MUL (p = 0.033) but there was no statistically significant association with vascular parameters. These results suggest that some bone marrow morphologic features prior TKI therapy might be indicators of favorable molecular response.

Stem cell decoupling underlies impaired lymphoid development during aging.

Mammalian aging is associated with multiple defects of hematopoiesis, most prominently with the impaired development of T and B lymphocytes. This defect is thought to originate in hematopoietic stem cells (HSCs) of the bone marrow, specifically due to the age-dependent accumulation of HSCs with preferential megakaryocytic and/or myeloid potential ("myeloid bias"). Here, we tested this notion using inducible genetic labeling and tracing of HSCs in unmanipulated animals. We found that the endogenous HSC population in old mice shows reduced differentiation into all lineages including lymphoid, myeloid, and megakaryocytic. Single-cell RNA sequencing and immunophenotyping (CITE-Seq) showed that HSC progeny in old animals comprised balanced lineage spectrum including lymphoid progenitors. Lineage tracing using the aging-induced HSC marker Aldh1a1 confirmed the low contribution of old HSCs across all lineages. Competitive transplantations of total bone marrow cells with genetically marked HSCs revealed that the contribution of old HSCs was reduced, but compensated by other donor cells in myeloid cells but not in lymphocytes. Thus, the HSC population in old animals becomes globally decoupled from hematopoiesis, which cannot be compensated in lymphoid lineages. We propose that this partially compensated decoupling, rather than myeloid bias, is the primary cause of the selective impairment of lymphopoiesis in older mice.